1. Field of the Invention:
The present invention relates to an improved closure mechanism in which a lid member is biased toward its closed position under the action of a biasing spring.
2. Description of the Prior Art:
Various types of electrical instruments and boxes include a closure structure comprising a lid member which is springly biased toward its closed position to prevent external dusts or other external matters from entering into the interior of each of the electrical instruments and boxes. In such a closure structure, the lid member is openable only when a preselected object is to be received. Such a closure structure is currently applied to the inlet opening of a floppy disk drive into which a floppy disk or disk cartridge is to be inserted or the inlet opening of a tape recorder, video recorder or CD device in which a cassette or disk is to be received.
Normally, the lid member is rotatably journalled on the backface of a panel and resiliently biased toward its closed position under the influence of spring means such as a leaf spring or the like. When it is wanted to insert a cartridge, cassette or disk into the interior of the device, the lid member can be forced to move inwardly so that the recording or recorded medium such as cartridge, cassette or disk will properly be inserted into the device or be removed therefrom.
In the prior art, however, the biasing spring is normally attached at one end to the backface of the panel with the opposite end thereof being hooked on a preselected point of action in the lid member. As the angle of the opened lid increases, therefore, the force of the biasing spring is increased so that the lid itself or the medium being inserted will be subjected to an excessive force when the medium is being inserted into the device. This may adversely influence the delicate recording or recorded medium. In other words, the recording or recorded medium may rapidly be degraded in service life since it is frequently used.
On the other hand, the biasing spring must properly be selected with respect to its spring constant and other performances such that the critical stress thereof will not be exceeded when said angle of the opened lid is increased. To properly design the biasing spring, however, the size of the biasing spring cannot help increasing. Thus, the leaf spring should undesirably be replaced by more expensive spring means such as coil spring or the like.